Cascading failures in large rectifiers or the myth of N-1

Large rectifiers depend on the parallel operation of significant numbers of parallel devices, either diodes or SCRs. Protection systems against cascading failure range from periodic visual inspection of an indicating system, to a wide variety of automatic alarm/trip systems. Historically, many of these systems have experienced cascading failures in spite of these systems, sometimes with catastrophic results. Many times, these failures occur only after many years of trouble free operation, when personnel fully aware of the system are no longer available. This paper will attempt to simulate this type of failure by using a matrix of thermal models for the fuses and devices. Statistical variations are entered to investigate the conditions leading to cascade failure, and the rates of the resulting cascade. Implications for protection systems and maintenance requirements are discussed.